The present invention concerns a metal tear-off cap which acts as a pressure closure means and can be secured by crimping on to the neck of a container. The cap has a tear-off strip extending around the cap surface, bounded by at least one tear line of reduced strength, a portion of the tear-off strip being covered by a foil.
Among the requirements for an ideal pressure closure means are that it should provide a good seal and it should be capable of ready removal without the use of a tool or implement.
Furthermore, the holding tabs produced by punching operations have the disadvantage that a hardening of the material occurs all around the cut edges. Such a hardening interferes with the functioning of the holding tab at the two points where the holding tab ends and the tear-off strip starts. The undesirable initial resistance which occurs when pulling off the tear-off strip greatly hinders opening of the container. An even greater disadvantage are tears in undesired directions produced as a result of the hardening, which prevent the proper functioning of the cap.
A further disadvantage of the known tear-off cap is that is their production a sensitive punching tool is required for punching out the holding tab. Since the holding tab is connected with the tear-off strip only at one narrow side for securing the foil or film the other three sides are free, there must be a tongue of appropriate shape in the matrix of an appropriate punching tool. This free narrow tongue of the tool is extremely sensitive to shock and pressure and therefore not well suited for robust mechanical production with several hundreds of punchings per minute.
This tool construction causes the further disadvantage that for the tear-off strip one must not exceed a minimum height required to fasten the free tongue in the matrix. Thus, the shape of the holding tab necessarily determines the height of the tear-off strip and therefore influences the total height of the cap. For this reason, the tear-off strip cannot be formed in a narrower size, which would make it possible to reduce the height of the cap. In the production of an enormously large number of caps, even a small reduction in height would afford a very large saving of material and cost. The closure means desirably should show whether the original contents of the bottle have been tampered with, and it must be hygienic and have no adverse effect at all upon the contents of the bottle. However, many existing pressure closure means fail to meet all the above requirements. Thus, for example, the known screw-on-caps do not guarantee that the original contents of the container have not been interfered with, and crowned caps cannot be removed without the use of an implement.
There are existing metal tear-off caps for sealing bottles and other containers, which have a tear-off strip, a portion of the tear-off strip being covered by a foil or film. German Pat. No. 1,204,544, for example, describes a tear-off cap, part of the tear-off strip of which is formed to provide a holding tab by means of a perforation of the cap skirt, the performation for said holding tab being covered by a foil also extending around the latter, which foil may project over the free end of said holding tab and can be secured to the holding tab through openings.
This and other tear-off caps with a tear-off strip and a punched-out holding tab -- with and without covering foil -- which are to be secured on to the neck of a container by crimping, have the disadvantage that they cannot be used as pressure closure means since the skirt surface of the cap is radially perforated along the length of the holding tab. If after closing a container by means of such a tear-off cap, an axial pressure is exerted upon the cap from inside by the contents the skirt surface normally compressed onto the neck of a container arches upwardly above the longer radial perforation despite the crimping; and the seal is destroyed.
In addition, the long radial perforation of the cap skirt interferes with the smooth passage of the cap through the feed mechanism and the machine. The cap skirt, which has reduced strength due to the perforation for the holding tab, tends to be dented at the high transport rates in the sorting and conveying systems, which damage the caps and interfere with their transportation.
This invention also concerns a metal tear-off cap which acts as a closure means capable of withstanding pressure and vacuum force and can be secured by crimping on to the neck of a container, which cap has a tear-off strip, extending around it and bounded by one tear line of reduced strength, and a film on a part of the tear-off strip, a narrow opening being formed at one point in the tear-off strip and at least one small aperture being formed therein farther round from said opening in the direction in which pull is applied, in which opening and aperture or apertures is secured a holding tab consisting of a tear-resisting piece of film, as previously described herein.
The previously described tear-off cap was developed as a closure means capable of withstanding pressure. Initially however, it was not thought that one and the same metal tear-off cap could be used as a closure means that could withstand both pressure and a vacuum force.
Generally, on the one hand caps are known which are intended to act as closure means capable of withstanding pressure, while on the other hand there are caps suitable for withstanding a vacuum force. Closure means for withstanding pressure are intended for sealing containers, especially bottles, the contents of which, e.g., carbonized beverages such as mineral water, lemonade, caffein-containing drinks and beer, generate an internal pressure. Closure means for withstanding vacuum force are used for sealing containers, the contents of which must be vacuum-sealed so as to keep them in good condition. Examples of products of this kind are milk, fruit, baby foods and meat.
The requirements imposed on closure means for withstanding pressure conflict with those imposed uon closure means for withstanding a vacuum force when these means are required to seal containers, especially bottles, and their contents in an air-tight manner. Whereas the sealing means for withstanding a vacuum force is automatically pressed on to the mouth of the bottle by the atmosphere on account of the reduced pressure in the bottle, a closure means for withstanding pressure must be connected so firmly to the mouth of the bottle that the closure cap cannot be lifted by the internal pressure.
When the closure means are opened, it is necessary in both cases to balance out the pressure difference betweeen the interior of the container and the surrounding atmosphere. For this purpose the closure means for withstanding pressure must lift i.e. permit the discharge of air at the commencement of the opening operation so that when this operation is completed the pressure in the container is relaxed. It is necessary to avoid removal of the closure means by the use of great force which might cause it to shoot off with the risk of injury to the user. When removing a closure means for withstanding a vacuum force, air has to be admitted to the container so as to balance out the pressure difference, since the closure means can only be readily removed after such equalization of pressure has been achieved. Thus, when removing the two kinds of closure means, the pressure is equalized in one direction in the one case and in the opposite direction in the other, i.e., air is released in the case of the closure means for withstanding pressure, and is admitted to the container in the case of pressure means for withstanding a vacuum force. Discharge of air is facilitated by the internal pressure, whereas the admission of air is rendered difficult by the relative exterior pressure.
Because of these conflicting requirements imposed on closure means for withstanding pressure and closure means for resisting a vacuum force, it has hitherto been thought that the ideal form of closure means for withstanding pressure must differ from that of closure means for withstanding a vacuum force.
The invention is directed to the object of providing simple and economical metal tear-off cap having a tear-off strip and foil on one portion of the tear-off band to be secured on to the neck of a container by crimping, which cap is useful as pressure closure means and meets all the above requirements to be met by a pressure closure means.
Another object of the present invention is to improve the aforementioned tear-off cap so that it can be used as a closure means for withstanding both pressure and a vacuum force.